1. Field of the Invention
The present invention relates to a composition for forming a silica based coating film, to a silica based coating film and a method for preparation thereof, and to electronic Parts.
2. Related Background Art
With progressive miniaturization of wiring by high integration in electronic device parts, including semiconductor elements such as LSIs, the increased signal delay time due to decreasing interconnect pitch has become a significant problem, and a demand therefore exists for greater heat resistance and mechanical properties, as well as low specific permittivity and shorter heat treatment steps for insulating materials of electronic parts.
Generally speaking, the signal propagation velocity (v) of wiring and the specific permittivity (∈) of an insulating material in contact with the wiring material are in the relationship represented by the following formula (3) (where k is a constant).v=k/√∈  (3)
In other words, high-speed signal propagation is achieved by increasing the frequency range used while also reducing the specific permittivity (∈) of the insulating material. For example, SiO2 films formed by CVD processes, having specific permittivities of about 4.2, have conventionally been used as materials for forming interlaminar insulating films, but from the standpoint of reducing device interconnect pitch and increasing LSI operation speed, materials exhibiting even lower permittivities have been desired.
Yet, the currently realized low permittivity materials include SiOF films with specific permittivities of about 3.5, formed by CVD. Other examples are organic SOG (Spin On Glass) and organic polymers used as insulating materials with specific permittivities of 2.5-3.0. Porous materials having gaps in the films are also promising as insulating materials with specific permittivities of 2.5 or lower, and a great deal of research and development has been conducted toward their application as LSI interlaminar insulating films.
As a method for forming such porous materials there has been proposed a method for creating low permittivities in organic SOG materials, as disclosed in Japanese Unexamined Patent Publication HEI No. 11-322992 and Japanese Unexamined Patent Publication HEI No. 11-310411. This method involves first forming a coating film using a composition comprising a polymer whose properties are such that it volatilizes or decomposes upon heating with hydrolytic polycondensation of a metal alkoxysilane, and then heating the coating film to form pores therein.